The present invention relates to ophthalmological surgery apparatus and methods and more particularly to an ophthalmological surgery apparatus and method for distorting the shape of the cornea for removing corneal tissue to change the curvature of the cornea to correct abnormal refractive conditions.
The human eye includes two focusing elements which are the cornea and the lens. The refractive power of the cornea is expressed in diopters and regions of the cornea are assigned Keratometry (K) values in relation to their degree of curvature. The normal human cornea has a K value that ranges from 38 to 50 diopters. The sum total of all K values is constant and if the shape of the cornea is distorted the K value in one region is decreased with a corresponding increase in a neighboring region.
In order to correct for abnormal refractive errors of the eye such as myopia, hyperopia, or astigmatism, glasses or contact lenses are used. An alternative to glasses or contact lenses is surgically altering or sculpting the shape of the cornea. Corneal sculpting involves the removal of external layers of the cornea which affects the radius of curvature of the cornea. Altering the radius of curvature of the cornea increases or decreases the dioptric power of the front surface of the cornea which corrects any abnormal refractive errors.
One approach of corneal sculpting is to remove the layers of the cornea by laser ablation. Laser ablation requires using ultraviolet laser radiation to selectively ablate the anterior surface of the cornea. The laser radiation is directed perpendicular to the cornea to penetrate into the stroma. However, problems are encountered by using this head-on approach for correcting the curvature of the cornea. For example, the laser radiation may penetrate to an excessive depth in the cornea. Therefore, it would be advantageous to remove layers of the cornea by tangential laser ablation of the cornea which does not use a head-on approach. Furthermore, although micromanipulators are known in the prior art, it would be advantageous to provide a micromanipulation which can be used in combination with a tangential laser ablation.